On paper, X6FC seems better than 602FC but to be honest, it’s really down to personal preference. I have X6FC + wise and they work well but the X6 has plastic cover on the 2 ends (with a drawer) and strings can easily be caught up in the gaps. I can see that’s not an issue with 602FC.
The clamps came with my X6 are 5-tooth universal clamps. In general they work fine except space between teeth is a bit narrow for crosses and sometimes causes damage to the mains. You can either order badminton clamps (4 teeth, cheap $70 each) or universal 4-tooth clamps which are default on all high-end Gamma machines. I like badminton clamps a bit better because they are cheaper (of course) and also they have slim profile so you can easily use it near racket frame, e.g. last mains or last cross. Its design is not as modern as the universal clamps and seems to have a bit less holding power.
Now onto the wise head, it’s a fine piece of equipment but if you want speed, it’s not a fast puller especially with pre-stretch on. But you don’t need to worry about it until you get down to 20 mins per string job. By then, you’ll probably want to sell and get a new machine already. On the other hand, XLT doesn’t mention anything about quick closing or speed so it’s not necessarily better.
Imho, if you are first time buyer, just go with the cheaper option with wise head. Think about yourself right now, it’s a lot easier to find somebody like you to sell and upgrade later.